Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyho...

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Bibliographic Details
Published in:Nature communications 2022-03, Vol.13 (1), p.1170-1170, Article 1170
Main Authors: Huang, Yuze, Fleming, Tristan G., Clark, Samuel J., Marussi, Sebastian, Fezzaa, Kamel, Thiyagalingam, Jeyan, Leung, Chu Lun Alex, Lee, Peter D.
Format: Article
Language:English
Subjects:
132/124
639/166/988
639/301/1034/1039
639/624/1075/1080
639/624/1107/510
639/766/259
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Diffusion
Gases
Humanities and Social Sciences
Lasers
multidisciplinary
Porosity
Powders
Science
Science (multidisciplinary)
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Summary:Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5–10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, bubbles undergo rapid growth due to pressure equilibration, then shrink due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The keyhole fluctuation and bubble evolution mechanisms revealed here may guide the development of control systems for minimising porosity. Understanding the keyhole porosity formation is important in laser powder bed fusion. Here the authors reveal the dynamics of keyhole fluctuation, and collapse that induces bubble formation with three main stages of evolution; growth, shrinkage, and being captured by the solidification front.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-022-28694-x